Damage threshold research of monocrystalline silicon solar cells under femtosecond laser illumination

Femtosecond laser with ultrashort pulse (35 fs) was first applied to investigate damage threshold of a monocrystalline silicon solar cell. Compared with a continuous-wave laser of the same central wavelength, a femtosecond laser pulse was found to have a slightly higher damage threshold. Unlike nanosecond or picosecond lasers, the femtosecond laser has heating pulse time equal to or shorter than the electron- phonon coupling time. Thus, the thermal non-equilibrium effect becomes obvious, and the heat conduction phenomenon no longer meets the law of Fourier. In the damage threshold experiments, a beam shaping technique was applied for a femtosecond laser to generate uniform intensity distribution, which could prevent experimental deviation caused by great concentrated intensity distribution of a conventional laser pulse with the Gaussian profile.